Duplexers (also referred to herein as duplex filters) and multiplexers (also referred to herein as multiplex filters) in modern communications systems require high out-of-band rejection and high isolation from any transmit (TX) to any receive (RX) port. The straightforward way to improve these rejection and isolation requirements is by means of re-optimization of the parameters governing the individual resonator elements in a filter or by increasing the order of the filter topology. Unfortunately, these methods more often than not result in an accompanying increase in in-band insertion loss.
As such, there is a need for systems and methods for improving out-of-band rejection and isolation between TX and RX ports of a duplexer or multiplexer while not impacting in-band insertion loss.